1. Field of the Invention
The present invention relates generally to devices that may be used to generate and control electrical discharges in ionization sources of analytical devices.
2. Description of the Related Art
Gas chromatography devices can separate a gas mixture into the mixture""s component gases and, after the separation, can quantify each component gas. A detector 10 used for analyzing a component gas is illustrated in FIG. 1A. The type of detector 10 illustrated in FIG. 1A is a discharge ionization detector that has previously been disclosed in U.S. Pat. No. 4,975,648 to Lawson et. al., the contents of which are incorporated herein by reference.
The detector 10 illustrated in FIG. 1A includes a housing 20 that has, formed within it, a discharge chamber 30, and ionization chamber 40, and an aperture 50 that connects the discharge chamber 30 and the ionization chamber 40. Also formed within the housing 20 are a surrounding gas inlet 60 that leads to the discharge chamber 30, a sample inlet 70 that leads to the ionization chamber 40 and a sample outlet 80 that also leads to the ionization chamber 40.
Within the discharge chamber 30 are a pair of spark-generating electrodes 90. One of the spark electrodes 90 has a small ball at the end thereof, while the other spark electrode 90 has a sharpened tip. Each of the spark electrodes 90 is connected to a separate pin 100 that supports the electrode 90 attached to it at a spatial location within the discharge chamber 30.
Each of the pins 100 is contained within a separate sheath 110 that protrudes from both sides of a sealing flange 120. The sealing flange 120 can be screwed into or otherwise fixed to one end of the housing 20.
Outside of the housing 20 and wrapped around each sheath 110 is a separate insulating plug 130. Each plug 130 leads to a separate wire 140 and each of the wires 140 is electrically connected to the same electronic circuit 150.
The electronic circuit 150 provides electrical current to each of the spark electrodes 90 during operation of the detector 10. The timing, duration and intensity of the sparks created between the electrodes 90 is controlled by the electronic circuit 150.
A collector electrode 160 and an emitter electrode 170 are position within the ionization chamber 40 of the detector 10 and are held in place via a bottom flange 180 that is fitted into the housing 20. A pair of wires 190 connect to the collector electrode 160 and the emitter electrode 170, respectively, and lead to a pair of electrical couplings 200. The wires 190 provide current to the collector electrode 160 and emitter electrode 170 when the detector 10 is in operation.
During operation, a surrounding or carrier gas, such as helium, is allowed to flow into the discharge chamber 30 through the surrounding gas inlet 60. The spark electrodes 90 are then provided with current from the electronic circuit 150 and are placed in close enough proximity to generate an electrical arc or spark across the electrodes 90. The electrical spark causes the surrounding gas to discharge photons and metastables at a characteristic energy level.
The photons and metastables then travel through the aperture 50 of the housing 20 and into the ionization chamber 40 that is filled with a gas that has been separated by the gas chromatography apparatus and that has been flowing into the ionization chamber 40 through the sample inlet 70. The photons and metastables then mix with and interact with the separated sample gas, cause electrons to be generated in the ionization chamber 40, cause a current to form between the collector electrode 160 and the emitter electrode 170, and allow for the concentration of the separated gas to be determined.
In order for the detector 10 to operate properly, the electrical discharges between the spark electrodes 90 are preferably chosen to be very stable. Instability in the discharges can cause serious deterioration of the analytical measurements being performed in the detector 10. Such deteriorations can include shifts or oscillations in the analytical measurement. Hence, the detector 10 shown in FIG. 1A is generally attached to an electronic circuit 150 that attempts to drive the discharge while enhancing the stability of the discharge.
FIG. 1B illustrates an electronic circuit 150 according to the related art that contains a resistor R, a first electrode 240, a second electrode 250, and a high voltage direct current (DC) power source 400. However, the DC discharges driven by the circuit 150 illustrated in FIG. 1B are unstable due to uncontrolled wandering of the space charge present in the discharge area over time.
In order to enhance the stability of the discharges compared to the circuit 150 illustrated in FIG. 1B, related art circuits 150 such as the one illustrated in FIG. 1C have been employed and have been disclosed in U.S. Pat. No. 5,153,519 to Wentworth et. al., the contents of which are incorporated herein by reference. The circuit 150 illustrated in FIG. 1C includes a resistor R, a first electrode 240 and a second electrode 250. According to such related art circuits 150, short, periodic, DC pulses 410 are used to produce discharges across the spark electrodes 90. However, the DC pulses generated by the circuit 150 illustrated in FIG. 1C results in discharge peak currents that are far greater than the average current.
Larger peak currents can cause deterioration and damage of the surface of the cathode spark electrode 90, particularly when noble gases with larger atomic masses are employed as the surrounding gas. Hence, the high peak currents generated by the circuit 150 illustrated in FIG. 1C require large cathode areas and large cross-sectional discharge areas.
Such large-area configurations are disfavored because they do not enable high the gas atoms to achieve high linear velocities between the discharge chamber 30 and the ionization chamber 40. Low linear velocities allow sample gas at high concentrations to diffuse into the discharge chamber 30 and quench the discharge. Hence, the detector""s 10 sample dynamic range is not optimized, as further discussed in U.S. Pat. No. 6,037,179 to Abdel-Rahman, the contents of which are incorporated herein by reference.
To summarize, the electronic circuit 150 illustrated in FIG. 1B and discussed above leads to instabilities in the DC discharges observed between the spark electrodes 90. On the other hand, the electronic circuit 150 illustrated in FIG. 1C requires high peak currents to effectuate ionization, can cause damage to the electrodes 90, and requires a large discharge cross-sectional area.
According to one embodiment, an electronic circuit that includes a first electrode for electrical connection to an ionization detector system, a second electrode for electrical connection to an ionization detector system, and a transformer electrically connected to the first electrode and to the second electrode for creating a spark between the first electrode and the second electrode.
According to another embodiment, a method of generating an electrical discharge for an ionization detector system that includes providing a first electrode and a second electrode, each electrically connected to an ionization system, providing a transformer electrically connected to the first electrode and the second electrode, inputting a DC voltage into the primary portion of the transformer, and generating a discharge current between the first electrode and the second electrode.